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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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This process also provides a mechanism for routers to declare themselves<br />

unavailable. They send an advertisement with a TTL value of zero.<br />

Time Exceeded (11)<br />

If this message is received from an intermediate router, it means that the time to<br />

live field of an <strong>IP</strong> datagram has expired.<br />

If this message is received from the destination host, it means that the <strong>IP</strong><br />

fragment reassembly time to live timer has expired while the host is waiting for a<br />

fragment of the datagram. The ICMP header code field can have the one of the<br />

following values:<br />

0 Transit TTL exceeded<br />

1 Reassembly TTL exceeded<br />

See Figure 3-35 for more details.<br />

0 8 16 31<br />

unused (zero)<br />

<strong>IP</strong> header - 64 bits of original data of the datagram<br />

Figure 3-35 ICMP: Time Exceeded<br />

Parameter Problem (12)<br />

This message indicates that a problem was encountered during processing of<br />

the <strong>IP</strong> header parameters. The pointer field indicates the octet in the original <strong>IP</strong><br />

datagram where the problem was encountered. The ICMP header code field can<br />

have the one of the following values:<br />

0 Unspecified error<br />

1 Required option missing<br />

See Figure 3-36 for more details.<br />

0 8 16 31<br />

pointer unused (zero)<br />

<strong>IP</strong> header - 64 bits of original data of the datagram<br />

Figure 3-36 ICMP: Parameter Problem<br />

Chapter 3. Internetworking protocols 115

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